The present invention relates to a process and apparatus for ceramising planar, transparent glass-ceramic sheets.
Planar transparent glass-ceramic sheets are of great economic interest today. They are used, for example, as windows in ovens. When so used, their appearance and their transparency is very important.
Up to now, the ceramising process of planar transparent glass-ceramic sheets has been practiced while the sheets were supported on a substrate or while the sheets were transported on rollers. During the ceramising process, an intimate contact occurs between the heat-softened, glass-ceramic sheet and the substrate such that the resultant glass-ceramic sheet takes the form of the substrate.
In the above manner, the surface of the resultant glass-ceramic sheet takes the form of the substrate including any uneveness of the substrate as well as undesirable particles, such as small stones or dust.
During the ceramising process, the material shrinks approximately one percent. Such shrinkage causes undesirable cracks and scratches. Furthermore, prior processes produce sheets of insufficient strength.